The invention relates to a plunger, in particular for forcing molten aluminum or brass out of a casting cylinder of a diecasting machine.
Known plungers of this type have a the inner cap inner cover face of which, leaving a coolant space clear, is located at a distance from the front face of the supporting body. The cap sits with its rear margin on an annular shoulder of the supporting body. When the cap has been screwed on, there is a gap between the internal thread of the cap and an extension of the supporting body at which the associated external thread starts. Experience shows that these caps work loose from the supporting body relatively easily during operation. In addition, the coolant space in the cap does not adequately cool the cover wall of the cap. The result of this is that the margin of the cover cap acts with great force against the inner surface of the casting cylinder and is closed. Normally, the instantaneous temperature of the surface of the cap is here around 300.degree. C., while the temperature of the molten aluminum is 700.degree. C. If the cap cools down again after work, a wedge-shaped gap develops between the peripheral margin of the cover wall of the cap, into which gap molten aluminum can penetrate and solidify there and considerably increases the friction between the plunger and cylinder and accordingly also the wear.